A trigger group includes all parts of the firearm that initiate the firing of the bullet. Parts include the trigger, which is usually a lever that is tripped by one or more fingers of the firing hand; the sear, which holds the hammer back until the trigger has been pulled; a disconnector, which keeps the hammer in place until the trigger is released and the sear takes over after a cycle of semi-automatic fire has occurred; and several springs throughout the group. The sear may be a separate part or can be a surface incorporated into the trigger. As the trigger is pulled, the sear slips, allowing the hammer to strike the firing pin to discharge a round.
The National Firearms Act, as interpreted by the Bureau of Alcohol, Tobacco, Firearms and Explosives Technology Branch, defines the pull of a trigger as a function, and the release of the trigger as a second function. As a result, a firearm that fires a shot upon the pull of a trigger and fires a second shot upon the release of the trigger is not a machine gun as defined by the National Firearms Act, 26 U.S.C. 5845(b), and is not subject to the associated legal restrictions.
An existing approach to a trigger system that fires one round with trigger pull and fires another round with trigger release is disclosed in U.S. Pat. No. 8,667,881 to Hawbaker. Hawbaker's trigger system provides one mode for normal semi-automatic operation and another mode that fires by pulling the trigger and fires a second round upon trigger release. However, Hawbaker's trigger system suffers from multiple disadvantages. First, a selector lever that is attached to the trigger must be manipulated within the trigger guard in order to change the mode of firing from semi-automatic to double fire. This attribute greatly increases the likelihood of an accidental discharge occurring from manipulating the selector lever. Second, once the trigger has been pulled in double fire mode, the user cannot place the firearm in safe mode, and instead must fire a second shot upon trigger release.
Therefore, a need exists for a new and improved trigger group for semi-automatic firearms that places the selector lever outside of the trigger guard and enables the firearm to be placed in safe mode even if the trigger has been pulled in double/binary fire mode. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the trigger group for semi-automatic firearms according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of providing a semi-automatic firearm with a fixed magazine without requiring modifications to the firearm.